Conversion devices that convert DC voltage outputted from a storage battery to AC voltage and provide the AC voltage to a load are often used as a backup power supply such as a UPS (Uninterruptible Power Supply) (see, for example, Patent Literature 1 (FIG. 1)). Such a conversion device includes a DC/DC converter for stepping up voltage of the storage battery and an inverter for performing conversion from DC to AC. The conversion device is capable of bidirectional operation, and normally, converts AC voltage outputted from an AC power supply such as a commercial power supply, to DC voltage adapted for charging, and charges the storage battery. In this case, the inverter operates as an AC/DC converter, and the DC/DC converter performs step-down operation.
A conversion device (power conditioner) is used also for converting DC power obtained from a DC power supply such as photovoltaic generation to AC power and performing system interconnection with an AC power system (see, for example, Patent Literature 2).